High-strength and ultra heat-resistant high entropy alloy (hea) matrix composites and method of preparing the same

ABSTRACT

A high-strength and ultra heat-resistant high entropy alloy (HEA) matrix composite material and a method of preparing the HEA matrix composite material are provided. The HEA matrix composite material may include at least four matrix elements among Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al, and a body-centered cubic (BCC) forming alloy element.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2016-0053871, filed on May 2, 2016, and Korean Patent Application No. 10-2017-0035200 filed on Mar. 21, 2017, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.

BACKGROUND 1. Field of the Invention

At least one example embodiment relates to a high-strength and ultra heat-resistant high entropy alloy (HEA) matrix composite material and a method of preparing the HEA matrix composite material.

2. Description of the Related Art

Existing alloy materials have been developed to enhance characteristics, for example, a hardness, a toughness, a heat resistance, a corrosion resistance, and the like, by addition of trace elements based on main metals, for example, Ti, Ni, and the like. Currently, such development of alloy materials by addition of trace elements has reached its limit.

Recently, research on high entropy alloys (HEAs) is being actively conducted. HEAs are reported to have excellent mechanical properties in comparison to existing metals due to effects of the HEAs, for example, a sluggish diffusion, a lattice distortion caused by a difference in size between elements, and a high mixing entropy by mixing at least four or five metal elements in near-equiatomic ratios.

A CoCrFeMnNi HEA reported in the journal Science in 2014 exhibits a fracture toughness of about 200 MPa·m^(0.5) and has physical properties close to three times that of a titanium alloy, and accordingly is gaining attention as next-generation extreme environment materials that may replace existing alloys.

In a high-energy milling process using a face-centered cubic (FCC) HEA with a high ductility, cold welding in a ball and a container may occur, which may lead to a reduction in a powder yield and a contamination by the ball.

In a composite HEA to which a reinforcing material is added, the reinforcing material may tend to be a reactive site that causes cold welding, and a yield may be severely reduced due to the cold welding. Thus, there is a desire for a new technology for reducing a cold welding phenomenon of a composite HEA using a powder metallurgy process.

SUMMARY

The present disclosure is to solve the foregoing problems, and an aspect provides a high entropy alloy (HEA) matrix composite material and a method of preparing the HEA matrix composite material which may significantly increase a yield by reducing a cold welding phenomenon while enhancing mechanical properties and heat resistance of an alloy.

However, the problems to be solved in the present disclosure are not limited to the foregoing problems, and other problems not mentioned herein would be clearly understood by one of ordinary skill in the art from the following description.

According to an aspect, there is provided a HEA matrix composite material including at least four matrix elements among Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al, and a body-centered cubic (BCC) forming alloy element.

The HEA matrix composite material may further include a reinforcing material. The reinforcing material may include at least one of a metal oxide, a metal silicide, a metal carbide, a metal nitride and a metal boride. Each of the metal oxide, the metal silicide, the metal carbide, the metal nitride and the metal boride may include at least one selected from the group consisting of Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, V, Nb, Mo, W, La and B.

The reinforcing material may be present in an amount of 0.01% by volume (vol %) to 50 vol % in the HEA matrix composite material.

A valence electron concentration (VEC) of the BCC forming alloy element may be less than or equal to “7.”

The BCC forming alloy element may be different from the matrix elements, and may include at least one of, Al, Cr, Mn, Mo, Nb, Ta, Ti, V and W.

The BCC forming alloy element may be present in an amount of 0.01% by moles (mol %) to 90 mol % in the HEA matrix composite material.

A VEC of the HEA matrix composite material may be less than or equal to “10.”

The HEA matrix composite material may further include a precipitate(s). The precipitate(s) may include at least one of a metal oxide, a metal silicide, a metal carbide, a metal nitride, a metal boride and an intermetallic compound. Each of the metal oxide, the metal carbide, the metal nitride, the metal boride and the intermetallic compound may include at least one of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, Nb, Ta, Mo, W, Ta, La and B.

The precipitate(s) may include at least one of Ni₃Nb, TiC, MoC, CrC, Cr₂₃C₆, Mo₂₃C₆, W₂₃C₆, Co₂₃C₆, Fe₂₃C₆, Mo₆C, W₆C, Co₆C, Ni₆C, Ni₃Al, Ni₃Ti, TiAl and Cr_(a)Mo_(b)Ni_(c) in which a, b and c are rational numbers.

According to another aspect, there is provided a method of preparing a HEA matrix composite material, including preparing a powder mixture by mixing a body-centered cubic (BCC) forming alloy element and at least four matrix elements selected from the group consisting of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al, forming a mechanically alloyed powder by mechanically alloying the powder mixture, and sintering the mechanically alloyed powder at a high temperature, wherein the forming of the mechanically alloyed powder includes bonding the BCC forming alloy element to at least a portion of the matrix elements.

The forming of the mechanically alloyed powder may include acquiring a HEA matrix composite material at a yield of 50% or greater using a high-energy ball mill.

The preparing of the powder mixture may include adding either a reinforcing material or a precipitate(s) forming element, or both to the powder mixture.

The method may further include, after the preparing of the powder mixture or the forming of the mechanically alloyed powder, adding a precipitate(s) forming element. The precipitate(s) forming element may include at least one of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Z, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, Nb, Mo, W, La and B.

The method may further include, after the sintering of the mechanically alloyed powder, forming a precipitate(s). The forming of the precipitate(s) may include forming the precipitate(s) by a heat treatment at a temperature of 300° C. to 1500° C.

The sintering of the mechanically alloyed powder may include sintering the mechanically alloyed powder at a temperature corresponding to 50% to 99% of a melting point of the mechanically alloyed powder.

Additional aspects of example embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the invention will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a flowchart illustrating a method of preparing a high entropy alloy (HEA) matrix composite material according to an example embodiment;

FIG. 2 is a diagram illustrating yields of powders of HEA matrix composite materials prepared in Examples 1, 2 and 3 and Comparative Examples 1 and 2 according to an example embodiment;

FIG. 3 is an X-ray diffraction (XRD) graph of HEA matrix composite materials prepared in Examples 1 to 3 according to an example embodiment;

FIG. 4 illustrates scanning electron microscopy (SEM) images of HEA matrix composite materials prepared in Examples 1 and 2 according to an example embodiment;

FIG. 5 is a graph illustrating a hardness of HEA matrix composite materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 according to an example embodiment; and

FIG. 6 is a graph illustrating a compressive strength of a HEA matrix composite material prepared in Example 1 according to an example embodiment.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. When it is determined detailed description related to a related known function or configuration they may make the purpose of the present disclosure unnecessarily ambiguous in describing the present disclosure, the detailed description will be omitted here. Also, terms used herein are defined to appropriately describe the example embodiments and thus may be changed depending on a user, the intent of an operator, or a custom of a field to which the present disclosure pertains. Accordingly, the terms must be defined based on the following overall description of this specification. Like reference numerals present in the drawings refer to the like elements throughout.

According to an example embodiment, a high entropy alloy (HEA) matrix composite material may be provided. The HEA matrix composite material may slightly increase a brittleness of a powder by adding a body-centered cubic (BCC) forming alloy element to a HEA matrix having a face-centered cubic (FCC) structure, to prevent a cold welding phenomenon and to increase a yield of an alloyed powder in a mechanical alloying process. Also, a precipitate(s) as well as a γ′ phase, an oxide, a carbide, a nitride, a boride and a silicide may be formed, and thus it is possible to enhance both a high-temperature stability and mechanical properties of an alloy.

The HEA matrix composite material may include a matrix element, and a BCC forming alloy element. The HEA matrix composite material may further include a reinforcing material and/or a precipitate(s).

The matrix element may be used to form a matrix HEA of the HEA matrix composite material, and may desirably be an element to form an alloy with an FCC structure. For example, all elements capable of forming an alloy with an FCC structure may be used as the matrix element without a limitation. The matrix element may include, for example, at least four of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al, and may desirably include, for example, a quaternary alloy such as CoCrFeNi, CoCrFeMn, CoCrFeCu, CoCrFeMo, CoCrFeV, CoCrFeNb, CuCrFeNi and CoCrCuNi; a quinary alloy such as CoCrFeNiMn, CoCrFeNiCu, CoCrFeNiMn, CoCrFeNiMo, CoCrFeNiV, CuCrFeNiMn, CoCrCuFeNi and CoCrFeNiNb; and a senary alloy such as CoCrFeNiMnMo, CoCrFeNiMnCu, CoCrFeNiMnV and CoCrFeNiMnNb.

The matrix element may be present in an amount of 5% by moles (mol %) to 35 mol % in the matrix HEA.

The BCC forming alloy element may be used to prevent cold welding and to enhance mechanical properties. For example, a BCC forming alloy element for reducing an average valence electron concentration (VEC) of an alloy to be less than or equal to “8” may be added to an alloy matrix, for example, an FCC alloy matrix with an average VEC greater than or equal to “8.” Thus, cold welding may be prevented in a mechanical alloying process and a yield of an alloyed powder may be significantly enhanced. Also, a contamination by a ball due to the cold welding may be prevented, and mechanical properties of an alloy may be enhanced.

For example, the BCC forming alloy element may be an element to reduce an average VEC of a HEA, and may have a VEC less than or equal to “7,” a VEC less than or equal to “6.8,” or a VEC less than or equal to “5.” The BCC forming alloy element may include, for example, at least one of Al, Cr, Mn, Mo, Nb, Ta, Ti, V and W. The BCC forming alloy element may be different from the matrix element. A VEC may refer to a sum of the number of peripheral electrons and the number of electrons included in a d-orbital. Based on the paper published by Guo et al. in the Journal of Applied Physics in 2011, an FCC phase and a BCC phase of a HEA may be determined by a VEC of a component of the HEA.

The BCC forming alloy element may be present in an amount of 0.01 mol % to 90 mol %, an amount of 0.1 mol % to 60 mol %, an amount of 0.1 mol % to 30 mol %, an amount of 0.1 mol % to 20 mol %, or an amount of 0.1 mol % to 5 mol % in the HEA matrix composite material. When the amount of the BCC forming alloy element is within the above ranges, a metal composite material that has excellent mechanical properties and that is used to prevent cold welding in a mechanical alloying process may be provided.

The reinforcing material may be used to enhance a strength of the HEA matrix composite material. The reinforcing material may include, for example, at least one of a metal oxide, a metal silicide, a metal carbide, a metal nitride and a metal boride. Each of the metal oxide, the metal silicide, the metal carbide, the metal nitride and the metal boride may include, for example, at least one of Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, V, Nb, Mo, W, La, and B.

The metal oxide may include, for example, at least one of Al₂O₃, SiO₂, TiO₂, ZrO₂, Ta₂O₅, MgO, BeO, BaTiO₃, ZnO, BaO, CrO₂, Y₂O₃, SnO₂, WO₂, W₂O₃, and WO₃. The metal carbide may include, for example, at least one of SiC, TiC, ZrC, HfC, VC, NbC, TaC, Mo₂C and WC. The metal nitride may include, for example, at least one of TiN, ZrN, HfN, VN, NbN, TaN, AlN, AlON, and Si₃N₄. The metal boride may include, for example, at least one of TiB₂, ZrB₂, HfB₂, VB₂, NbB₂, TaB₂, WB₂, MoB₂, B₄C and LaB₆.

The reinforcing material may be present in an amount of 0.01% by volume (vol %) to 50 vol % and desirably in an amount of 0.05 vol % to 10 vol % in the HEA matrix composite material. When the amount of the reinforcing material is within the above ranges, the reinforcing material may be uniformly dispersed in an alloy matrix and a strength of a metal composite material may be enhanced.

The precipitate(s) may enhance high-temperature properties of a metal composite material so that a HEA matrix composite material applicable as a material for a high temperature may be formed. The precipitate(s) may be formed by, for example, at least one of a matrix element, a BCC forming alloy element and an added precipitate(s) forming element or material. The precipitate(s) may include a γ′ phase, and/or at least one of an oxide, a carbide, a nitride, a boride, a silicide and an intermetallic compound.

For example, the γ′ phase may be a crystalline phase that includes at least one element or at least two elements among a BCC forming alloy element, a precipitate(s) forming element and a matrix element dispersed in a matrix HEA. The γ′ phase may include, for example, at least one of Ni₃Al, Ni₃Ti and TiAl.

The oxide, the carbide, the nitride, the boride, the silicide and the intermetallic compound in the precipitate(s) may include, for example, at least one of a metal oxide, a metal silicide, a metal carbide, a metal nitride, a metal boride and an intermetallic compound. Each of the metal oxide, the metal silicide, the metal carbide, the metal nitride, the metal boride and the intermetallic compound may include, for example, at least one of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, If, Nb, Mo, W, La and B.

The metal carbide may include, for example, TiC, MoC, CrC, Cr₂₃C₆, Mo₂₃C₆, W₂₃C₆, Co₂₃C₆, Fe₂₃C₆, Mo₆C, W₆C, Co₆C, Ni₆C, and the like.

The intermetallic compound may be, for example, an intermetallic compound with at least two elements. The intermetallic compound with at least two elements may include, for example, M1 _(a)M2 _(b) and M1 _(a)M2 _(b)M3 _(c) (in which M1, M2 and M3 are selected from Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Zr, Ta, Mg, Bo, Ba, Zn, Cr, Y, Sn, W, Hf, Nb, Mo, W, La, and B, and a, b and c denote the same rational number or different rational numbers and may be a rational number less than or equal to “100”). For example, M1 _(a)M2 _(b) may be Ni₃Nb, Ni₃Al, Ni₃Ti, TiAl, and the like, and M1 _(a)M2 _(b)M3 _(c) may be a CrMoNi-based compound, such as Cr_(a)Mo_(b)Ni_(c), and the like.

In an example, the precipitate(s) may be formed by either a matrix element or a BCC forming alloy element, or both in a process of alloying the HEA matrix composite material, and/or may be formed by adding a precipitate(s) forming element before or after a mechanically alloyed powder is formed. In another example, the precipitate(s) may be formed by sintering the mechanically alloyed powder and/or by a heat treatment after the sintering.

For example, the precipitate(s) forming element may be the same as or different from a matrix element. The precipitate(s) forming may include, for example, at least one of Co, Cr, Fe, Mn, Cu, Mo, V, Nb, Ni, Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, V, Nb, Ta, Mo, W, Ta, La, and B. The precipitate(s) forming element may be present in an amount exceeding 0 mol % and less than or equal to 300 mol %, and desirably in an amount of 1 mol % to 100 mol % with respect to the matrix element and/or the BCC forming alloy element.

The HEA matrix composite material may have an average VEC less than or equal to “10,” an average VEC of “5” to “8,” or an average VEC of “6” to “7.5.” For example, the matrix element may form an FCC structure. Accordingly, when a BCC forming alloy element with a lower VEC than that of the matrix element is added, an average VEC of an alloy matrix composite material may be reduced and the alloy matrix composite material may have both a BCC structure and an FCC structure. Also, by reducing the average VEC of the alloy matrix composite material, it is possible to prevent cold welding between matrix alloy elements in a mechanical alloying process.

According to an example embodiment, a method of preparing a HEA matrix composite material may be provided. In the method, a BCC forming alloy element may be added to a matrix element or a reinforcing material may be additionally added, and thus it is possible to enhance a mechanical strength and a yield of the HEA matrix composite material. Also, a precipitate(s) may be additionally added, and thus it is possible to enhance a high-temperature characteristic of the HEA matrix composite material.

FIG. 1 is a flowchart illustrating a method of preparing a HEA matrix composite material according to an example embodiment. The method of FIG. 1 may include operation 110 of preparing a powder mixture, operation 120 of forming a mechanically alloyed powder, and operation 130 of sintering the mechanically alloyed powder at a high temperature.

In operation 110, the powder mixture may be prepared by mixing a matrix element and a BCC forming alloy element. The matrix element and the BCC forming alloy element have been described above in the description of the HEA matrix composite material. A powder mixing method applicable in the technical field of the present disclosure may be used in operation 110, and accordingly further description thereof is not repeated herein.

In operation 120, the mechanically alloyed powder may be formed by mechanically alloying the powder mixture. Operation 120 may be performed to prevent cold welding of powders in a mechanical alloying process by adding the BCC forming alloy element so as to increase a yield of an alloy, and to prevent impurities from flowing into the alloy by preventing a contamination by a ball mill.

In an example, in operation 120, the BCC forming alloy element may be bonded to at least a portion of the matrix element and may be dispersed in the alloy matrix. In another example, the BCC forming alloy element may be bonded to at least a portion of the matrix element, to form a BCC alloy. The BCC alloy may also be dispersed in the alloy matrix.

In operation 110, a reinforcing material (for example, a reinforcing material forming element and/or material) may be additionally added to the powder mixture. The reinforcing material has been described above.

For example, operation 120 may be performed within 120 hours, for a period of 1 hour to 120 hours, or a period of 10 hours to 50 hours.

In operation 120, the HEA matrix composite material may be provided at a yield greater than or equal to 50%, a yield greater than or equal to 60%, a yield greater than or equal to 80%, or a yield greater than or equal to 90%.

In operation 120, a high-energy ball mill may be used. For example, a vibration mill, a planetary mill, an attrition mill, and the like may be used, however, there is no limitation thereto.

In operation 130, the mechanically alloyed powder may be sintered at a high temperature so that the mechanically alloyed powder may be formed of bulk materials. For example, in operation 130, a normal sintering method, a reaction sintering method, a pressurizing sintering method, an isostatic pressure sintering method, a gas pressure sintering method, or a high-temperature pressurizing sintering method may be used, however, there is no limitation thereto.

In operation 130, the mechanically alloyed powder may be sintered at a temperature that corresponds to 50% to 99%, 50% to 80%, 60% to 80%, 70% to 80%, 50% to 70%, 60% to 70%, or 50% to 60% of a melting point of the mechanically alloyed powder.

Operation 130 may be performed in an atmosphere including at least one of air, nitrogen, carbon and boron for 60 hours or less, for a period of 1 minute to 60 hours, a period of 5 minutes to 10 hours, a period of 5 minutes to 5 hours or a period of 5 minutes to 1 hour.

The method may further include operation 140 of adding a precipitate(s) forming element. Operation 140 may be performed after operation 110 to add and mix the precipitate(s) forming element and the powder mixture, and/or operation 140 may be performed after operation 120 to add and mix the precipitate(s) forming element and the mechanically alloyed powder and to further perform mechanical alloying as necessary.

In operation 140, the precipitate(s) forming element may be added in an amount exceeding 0 mol % and less than or equal to 300 mol %, and desirably in an amount of 1 mol % to 100 mol %, with respect to the matrix element and/or the BCC forming alloy element.

The method may further include operation 150 of forming a precipitate(s). In operation 150, the precipitate(s) may be formed by a heat treatment of the mechanically alloyed powder sintered in operation 130. For example, the heat treatment may be performed at a temperature of 300° C. to 1500° C. for 60 hours or less, for a period of 1 minute to 60 hours, a period of 10 minutes to 50 hours, a period of 1 hour to 20 hours, or a period of 1 hour to 10 hours. When a temperature and a period of time for the heat treatment are within the above ranges, the precipitate(s) may be efficiently formed, and a high-temperature characteristic of an alloy material may be enhanced. For example, in operation 150, the heat treatment may be performed in an atmosphere including at least one of air, nitrogen, carbon and boron.

Example 1

Mechanical alloying was performed using a planetary mill for 24 hours, to prepare an Al_(0.3)CoCrFeMnNi HEA powder to which 3 vol % of Y₂O₃ was added. About 5.7 mol % of Al was added as a BCC forming alloy element. A yield of the prepared Al_(0.3)CoCrFeMnNi HEA powder is shown in FIG. 2.

The prepared 3 vol % Y₂O₃/Al_(0.3)CrCrFeMnNi HEA powder was sintered at 900° C. for 5 minutes using a spark plasma sintering method, to prepare a sintered alloy. A phase and a microstructure of the sintered alloy were analyzed and a hardness and a compressive strength of the sintered alloy were measured as shown in FIGS. 3 to 6. The microstructure was obtained by a scanning electron microscope (SEM).

Example 2

Mechanical alloying was performed using a planetary mill for 24 hours, to prepare an Al_(0.3)CoCrFeMnNi HEA powder to which 5 vol % of TiC was added. About 5.7 mol % of Al was added as a BCC forming alloy element. A yield of the prepared Al_(0.3)CoCrFeMnNi HEA powder is shown in FIG. 2.

The prepared 5 vol % TiC/Al_(0.3)CoCrFeMnNi HEA powder was sintered at 900° C. for 5 minutes using a spark plasma sintering method, to prepare a sintered alloy. A phase and a microstructure of the sintered alloy were analyzed and a hardness of the sintered alloy was measured as shown in FIGS. 3 to 5.

Example 3

Mechanical alloying was performed using a planetary mill for 24 hours, to prepare a Mo_(0.8)CoCrFeMnNi HEA powder. About 13.8 mol % of Mo was added as a BCC forming alloy element. A yield of the prepared Mo_(0.8)CoCrFeMnNi HEA powder is shown in FIG. 2.

The prepared Mo_(0.8)CoCrFeMnNi HEA powder was sintered at 900° C. for 5 minutes using a spark plasma sintering method, to prepare a sintered alloy. A phase and a microstructure of the sintered alloy were analyzed and a hardness of the sintered alloy was measured as shown in FIGS. 3 to 5.

Comparative Example 1

An alloyed powder was prepared in the same manner as in Example 1 except that a CoCrFeNiMn HEA was formed. A yield of the alloyed powder is shown in FIG. 2. The prepared CoCrFeNiMn HEA powder was sintered at 900° C. for 5 minutes using a spark plasma sintering method, to prepare a sintered alloy. A hardness of the sintered alloy was measured as shown in FIG. 5.

Comparative Example 2

An alloyed powder was prepared in the same manner as in Example 1 except that a CoCrFeNiMn HEA to which 3 vol % of Y₂O₃ was added was formed. A yield of the alloyed powder is shown in FIG. 2. The prepared CoCrFeNiMn HEA was sintered at 900° C. for 5 minutes using a spark plasma sintering method, to prepare a sintered alloy. A hardness of the sintered alloy was measured as shown in FIG. 5.

Referring to FIG. 2, the CoCrFeNiMn HEA of Comparative Example 1 to which Al was not added as a BCC alloying element has a yield of 17.6%, and the CoCrFeNiMn HEA of Comparative Example 2 to which 3 vol % of Y₂O₃ was added has a yield of 16.4%, whereas the Al_(0.3)CoCrFeMnNi HEA powder of Example 1 to which 3 vol % of Y₂O₃ was added has a yield of 81.2% that is superior to the yields of the CoCrFeNiMn HEAs of Comparative Examples 1 and 2. This is because most of powders are entangled in a ball and a container due to cold welding in a mechanical alloying process, thereby lowering a yield of the alloyed powder. However, since Al was added as a BCC alloying element to the 3 vol % Y₂O₃/Al_(0.3)CoCrFeMnNi HEA powder in Example 1, it is possible to reduce the cold welding by enhancing a brittleness of the powder, and possible to obtain an alloyed powder at a high yield.

In an X-ray diffraction (XRD) graph of FIG. 3, a phase analysis of the sintered alloy is shown. It can be found from the XRD graph that Mo was added to the sintered alloy prepared in Example 3, to form a BCC phase and to form a precipitate that includes Cr, Mo and Ni.

Referring to FIG. 4, it can be found that reinforcing materials are uniformly dispersed as shown in SEM images that show the microstructures of the sintered alloys of Examples 1 and 2.

Referring to FIG. 5, it can be found that the hardness of the Al_(0.3)CoCrFeMnNi alloy to which 3 vol % of Y₂O₃ was added in Example 1 and the hardness of the Al_(0.3)CoCrFeMnNi alloy to which 5 vol % of TiC was added in Example 2 were enhanced in comparison to the CoCrFeNiMn alloy of Comparative Example 1 and the CoCrFeNiMn alloy of Comparative Example 2 to which 3 vol % of Y₂O₃ was added. Referring to FIG. 6, it can be found that the 3 vol % Y₂O₃/Al_(0.3)CoCrFeMnNi alloy of Example 1 has a high compressive strength, which may indicate that mechanical properties may be enhanced by adding Al and a reinforcing material and a powder yield may also be enhanced by adding Al as a BCC alloying element to a HEA.

Thus, a BCC forming alloy element and a reinforcing material may be added, to enhance a heat resistance and mechanical properties of a HEA matrix composite material, to prevent cold welding in a mechanical alloying process, and to increase a yield of an alloyed powder.

According to example embodiments, it is possible to prevent cold welding by adding a BCC forming alloy element to a HEA matrix, to increase a yield of an alloyed powder of a HEA matrix composite material. Also, it is possible to enhance a heat resistance and mechanical properties of the HEA matrix composite material by additionally adding a reinforcing material.

Although the example embodiments have been described with reference to the accompanying drawings, the present disclosure is not limited to the described example embodiments. Instead, it would be appreciated by one of ordinary skill in the art that various modifications and changes may be made to these example embodiments without departing from the principles and spirit of the present disclosure. It is intended therefore that the scope of the present invention not be limited to the foregoing embodiments, but be defined by the claims appended hereto and their equivalents. 

What is claimed is:
 1. A high entropy alloy (HEA) matrix composite material comprising: at least four matrix elements selected from the group consisting of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al; and a body-centered cubic (BCC) forming alloy element.
 2. The HEA matrix composite material of claim 1, further comprising: a reinforcing material comprising at least one selected from the group consisting of a metal oxide, a metal silicide, a metal carbide, a metal nitride and a metal boride, wherein each of the metal oxide, the metal silicide, the metal carbide, the metal nitride and the metal boride comprises at least one selected from the group consisting of Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, V, Nb, Mo, W, La and B.
 3. The HEA matrix composite material of claim 2, wherein the reinforcing material is present in an amount of 0.01% by volume (vol %) to 50 vol % in the HEA matrix composite material.
 4. The HEA matrix composite material of claim 1, wherein a valence electron concentration (VEC) of the BCC forming alloy element is less than or equal to “7.”
 5. The HEA matrix composite material of claim 1, wherein the BCC forming alloy element is different from the matrix elements, and comprises at least one selected from the group consisting of, Al, Cr, Mn, Mo, Nb, Ta, Ti, V and W.
 6. The HEA matrix composite material of claim 1, wherein the BCC forming alloy element is present in an amount of 0.01% by moles (mol %) to 90 mol % in the HEA matrix composite material.
 7. The HEA matrix composite material of claim 1, wherein a VEC of the HEA matrix composite material is less than or equal to “10.”
 8. The HEA matrix composite material of claim 1, further comprising: a precipitate(s) comprising at least one selected from the group consisting of a metal oxide, a metal silicide, a metal carbide, a metal nitride, a metal boride and an intermetallic compound, wherein each of the metal oxide, the metal carbide, the metal nitride, the metal boride and the intermetallic compound comprises at least one selected from the group consisting of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, Nb, Mo, W, La and B.
 9. A method of preparing a high entropy alloy (HEA) matrix composite material, the method comprising: preparing a powder mixture by mixing a body-centered cubic (BCC) forming alloy element and at least four matrix elements selected from the group consisting of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Ta, Ti, Zr, W, Si, Hf and Al; forming a mechanically alloyed powder by mechanically alloying the powder mixture; and sintering the mechanically alloyed powder at a high temperature, wherein the forming of the mechanically alloyed powder comprises bonding the BCC forming alloy element to at least a portion of the matrix elements.
 10. The method of claim 9, wherein the forming of the mechanically alloyed powder comprises acquiring a HEA matrix composite material at a yield of 50% or greater using a high-energy ball mill.
 11. The method of claim 9, wherein the preparing of the powder mixture comprises adding a reinforcing material to the powder mixture.
 12. The method of claim 9, further comprising, after the preparing of the powder mixture or the forming of the mechanically alloyed powder: adding a precipitate(s) forming element, wherein the precipitate(s) forming element comprises at least one selected from the group consisting of Co, Cr, Fe, Ni, Mn, Cu, Mo, V, Nb, Al, Si, Ti, Zr, Ta, Mg, Be, Ba, Zn, Cr, Y, Sn, W, Hf, Nb, Ta, Mo, W, Ta, La and B.
 13. The method of claim 9, further comprising, after the sintering of the mechanically alloyed powder: forming a precipitate(s), wherein the forming of the precipitate(s) comprises forming the precipitate(s) by a heat treatment at a temperature of 300° C. to 1500° C.
 14. The method of claim 9, wherein the sintering of the mechanically alloyed powder comprises sintering the mechanically alloyed powder at a temperature corresponding to 50% to 99% of a melting point of the mechanically alloyed powder. 